The present invention relates to a microprocessor and, more particularly, to improvements in the external bus interface of a microprocessor.
There are microprocessors (micro-controllers) equipped with an external bus capable of being directly connected to various semiconductor memories including a synchronous DRAM (dynamic random access memory). Such microprocessors are discussed illustratively in Nikkei Electronics published by Nikkei-MacGrow-Hill, Inc. (Feb. 14, 1994, pp. 79-91).
So-called PC cards such as memory cards and I/O cards are row in widespread use. The conditions for interfacing the PC cards to microprocessors and the like have been standardized by the Japan Electronics Industry Development Association (JEIDA) and the Personal Computer Memory Card International Association (PCMCIA). The PC card interface includes the IC memory card and I/O card interface provisions for the 68-pin type, stipulated in xe2x80x9c6. Electrical Interface Specificationsxe2x80x9d of the Guideline Ver. 4.1. The PC card interface is implemented illustratively by use of a dedicated integrated circuit(IC) chip such as the 82365SL.
In conventional microprocessors, the bus for coupling to PC cards is furnished independently of the bus for connecting semiconductor memories. Furthermore, the PC cards are connected to the bus via the dedicated IC chip which controls the PC card interface. This entails a complicated bus constitution and an increasing number of design steps required where the PC card interface is to be incorporated in personal computers and portable data processing terminals. With more parts to be attached externally to the microprocessor because of the PC card interface, it takes more time to develop personal computers and portable data processing terminals. The prolonged period of product development hampers these products from being reduced in manufacturing costs.
It is therefore an object of the present invention to provide a microprocessor that is easy and convenient to use. Another object of the invention is to provide a microprocessor which, when incorporated in a personal computer or like product equipped with the PC card interface, allows the computer to be designed in a reduced time and with fewer parts to be attached externally thereto, whereby the manufacturing cost of the computer as a whole is reduced.
These and other objects, features and advantages of the invention will become more apparent upon a reading of the following description and appended drawings.
The invention disclosed in this specification is outlined as follows: according to one aspect of the invention, there is provided a microprocessor to be incorporated in a personal computer, a portable data processing terminal or the like, the microprocessor being furnished with a bus state controller. The bus state controller BSC, connected to an external bus, controls parallelly the interfaces for various semiconductor memories such as a ROM, a burst ROM, an SRAM, a PSRAM, a DRAM and in synchronous DRAM, as well as for PC cards such as a memory card and an I/O card. The bus state controller BSC includes a control register (PCR) for controlling the time to set up PC card start signals (-OE, -WE) where a synchronous DRAM is connected.
Preferably, the inventive microprocessor has the address space of the external bus divided into a predetermined number of areas to which various semiconductor memories and PC cards are fixedly assigned. The address space areas are assigned independently two kinds of physical addresses: those in effect when the I/O card functions as an I/O device, and those used when the I/O card acts as a memory. The microprocessor is preferably equipped with a memory management unit for converting an internal logical address to a physical address applicable to the external bus.
The foregoing objects are attained through the use of the above-outlined means for the following reasons: the inventive microprocessor is free of constraints of physical address assignments and requires fewer parts to be attached externally thereto for interface control. As such, the microprocessor has various semiconductor memories and PC cards such as a memory card and an I/O card connected directly and concurrently to a bus external to the microprocessor. Consequently, the microprocessor becomes more convenient to use. When incorporated in a personal computer equipped with PC card interfaces, the microprocessor helps reduce the number of steps to design the computer. With its externally attached parts reduced in quantity, the microprocessor costs less to manufacture.
The bus state controller BSC has the control register (PCR) for controlling the time to set up PC card start signals (-OE, -WE) where the synchronous DRAM is connected. The control register arrangement makes it possible to control the fall of a clock signal CKIO for an output enable signal (-OE) and a write enable signal (-WE) used as the PC card start signals, and to control the time to set up address signals. As a result, even if a PC card and a synchronous DRAM are connected concurrently to the inventive microprocessor MPU, the microprocessor may access both the PC card and the DRAM with no difficulty.